Video transmission system

ABSTRACT

A video transmission system is disclosed. The video transmission system comprises a multi-drop bus, a first source driving chip, a second source driving chip and a timing controller. The first source driving chip comprises a first source driving circuit and a first terminal circuit. The first terminal circuit is coupled to the multi-drop bus and the first source driving circuit for providing a first terminal resistor. The second source driving chip comprises a second source driving circuit and a second terminal circuit. The second terminal circuit is coupled to the multi-drop bus and the second source driving circuit for providing a second terminal resistor. The timing controller is coupled to the first source driving chip and the second source driving chip via the multi-drop bus.

This application claims the benefit of Taiwan application Serial No. 103116386, filed May 8, 2014, the subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates in general to a transmission system, and more particularly to a video transmission system.

Description of the Related Art

Display is an electronic product that has been widely used. To provide truthful and vivid frames, both the resolution and the refresh rate of the display must be increased, and display of high-speed applications is thus provided. Facing the requirements of high-speed applications, the reflection and decay of transmission lines will make it difficult to increase the refresh rate of the display. Therefore, the transmission lines must have suitable impedance matching.

In the multi-drop configuration of the display, single output channel of the timing controller is coupled to a plurality of source driving chips via a pair of transmission lines. According to the conventional method, a terminal resistor is disposed on the part of a printed circuit board closest to an input terminal of a source driving chip to match the impedance of the transmission line. However, when the terminal resistor disposed on the printed circuit board does not match the impedance of the transmission line, signals will be reflected and result in transmission distortion.

SUMMARY OF THE INVENTION

The invention is directed to a video transmission system.

According to one embodiment of the present invention, a video transmission system is disclosed. The video transmission system comprises a multi-drop bus, a first source driving chip, a second source driving chip and a timing controller. The first source driving chip comprises a first source driving circuit and a first terminal circuit. The first terminal circuit is coupled to the multi-drop bus and the first source driving circuit for providing a first terminal resistor. The second source driving chip comprises a second source driving circuit and a second terminal circuit. The second terminal circuit is coupled to the multi-drop bus and the second source driving circuit for providing a second terminal resistor. The timing controller is coupled to the first source driving chip and the second source driving chip via the multi-drop bus.

The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment (s). The following description is made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a video transmission system according to a first embodiment.

FIG. 2 is a partial schematic diagram of a video transmission system according to a first embodiment.

FIG. 3 is a timing diagram of video data transmission according to a first embodiment.

FIG. 4 is a schematic diagram of a terminal circuit according to a first embodiment.

FIG. 5 is a schematic diagram of a setting command according to a first embodiment.

FIG. 6 is a schematic diagram of all terminal circuits concurrently providing terminal resistors.

FIG. 7 is a schematic diagram of some of the terminal circuits providing a terminal resistor.

FIG. 8 is a schematic diagram of all terminal circuits concurrently not providing any terminal resistors.

FIG. 9 is a timing diagram of video data transmission according to a second embodiment.

FIG. 10 is a schematic diagram of a terminal circuit according to a third embodiment.

FIG. 11 is a schematic diagram of a setting command according to a third embodiment.

FIG. 12 is a schematic diagram of a video transmission system according to a fourth embodiment.

FIG. 13 is a schematic diagram of a video transmission system according to a fifth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

Referring to FIG. 1, a schematic diagram of a video transmission system according to a first embodiment is shown. The video transmission system 1 comprises a multi-drop bus 11, a multi-drop bus 12, source driving chips 13 a˜13 c, source driving chips 14 a˜14 c and a timing controller 15. The timing controller 15 is coupled to the source driving chips 13 a˜13 c via the multi-drop bus 11, and is coupled to the source driving chips 14 a˜14 c via the multi-drop bus 12. The source driving chip 13 a comprises a terminal circuit 131 a and a source driving circuit 132 a. The terminal circuit 131 a is coupled to the multi-drop bus 11 and the source driving circuit 132 a for providing a terminal resistor. The source driving chip 13 b comprises a terminal circuit 131 b and a source driving circuit 132 b. The terminal circuit 131 b is coupled to the multi-drop bus 11 and the source driving circuit 132 b for providing a terminal resistor. The source driving chip 13 c comprises a terminal circuit 131 c and a source driving circuit 132 c. The terminal circuit 131 c is coupled to the multi-drop bus 11 and the source driving circuit 132 c for providing a terminal resistor.

The source driving chip 14 a comprises a terminal circuit 141 a and a source driving circuit 142 a. The terminal circuit 141 a is coupled to the multi-drop bus 12 and the source driving circuit 142 a for providing a terminal resistor. The source driving chip 14 b comprises a terminal circuit 141 b and a source driving circuit 142 b. The terminal circuit 141 b is coupled to the multi-drop bus 12 and the source driving circuit 142 b for providing a terminal resistor. The source driving chip 14 c comprises a terminal circuit 141 c and a source driving circuit 142 c. The terminal circuit 141 c is coupled to the multi-drop bus 12 and the source driving circuit 142 c for providing a terminal resistor.

The multi-drop bus 11 and the multi-drop bus 12 transmit data according to such as the format of mini low-voltage differential signaling (mini-LVDS). The multi-drop bus 11 comprises transmission lines 11 a and 11 b. The multi-drop bus 12 comprises transmission lines 12 a and 12 b. The timing controller 15 is coupled to the source driving chips 13 a˜13 c via the transmission lines 11 a and 11 b. The timing controller 15 is coupled to the source driving chips 14 a˜14 c via the transmission lines 12 a and 12 b.

Refer to both FIG. 2 and FIG. 3. FIG. 2 is a partial schematic diagram of a video transmission system according to a first embodiment. FIG. 3 is a timing diagram of video data transmission according to a first embodiment. The source driving circuit 132 a comprises a receiving circuit 1321 a, a driving signal generator 1322 a and a register 1323 a. The source driving circuit 132 b comprises a receiving circuit 1321 b, a driving signal generator 1322 b and a register 1323 b. The source driving circuit 132 c comprises a receiving circuit 1321 c, a driving signal generator 1322 c and a register 1323 c.

Bus signal LV0 represents the setting command and video data transmitted via the multi-drop bus 11. The timing controller 15 transmits the bus signal LV0 to the source driving chips 13 a˜13 c via the multi-drop bus 11. Download period LD indicates the start of each frame period TF. The timing controller 15 outputs the download signal LD to the source driving chip 13 a. When the download signal LD appears, the receiving circuit 1321 a receives a setting command C1 via the multi-drop bus 11 during a setting period TS1 and receives a video data D1 via the multi-drop bus 11 during a transfer period TD1. The transfer period TD1 is behind the setting period TS1. During the setting period TS1, the terminal circuit 131 a provides a terminal resistor according to the setting command C1 and further connects the terminal resistor to the multi-drop bus 11. The driving signal generator 1322 a outputs a corresponding source driving signal according to the video data D1. After the transfer period TD1 ends, the source driving chip 13 a outputs a data input/output starting signal DIO1 to the source driving chip 13 b.

After the data input/output starting signal DIO1 activates the source driving chip 13 b, the receiving circuit 1321 b receives a setting command C2 via the multi-drop bus 11 during a setting period TS2, and receives a video data D2 via the multi-drop bus 11 during a transfer period TD2. The transfer period TD2 is behind the setting period TS2. During the setting period TS2, the terminal circuit 131 b provides a terminal resistor according to the setting command C2 and further connects the terminal resistor to the multi-drop bus 11. The driving signal generator 1322 b outputs a corresponding source driving signal to the panel according to the video data D2. After the transfer period TD2 ends, the source driving chip 13 b outputs a data input/output starting signal DIO2 to the source driving chip 13 c.

After the data input/output starting signal DIO2 activates the source driving chip 13 b, the receiving circuit 1321 c receives a setting command C3 via the multi-drop bus 11 during a setting period TS3 and receives a video data D3 via the multi-drop bus 11 during a transfer period TD3. The transfer period TD3 is behind the setting period TS3. During the setting period TS3, the terminal circuit 131 c provides a terminal resistor according to the setting command C3 and further connects the terminal resistor to the multi-drop bus 11. The driving signal generator 1322 c outputs a corresponding source driving signal according to the video data D3.

In the above embodiments, the terminal circuits 131 a˜131 c sequentially provide terminal resistors which can be connected in parallel via the multi-drop bus 11. However, the practical application is not limited to the above exemplification. In another embodiment, the terminal circuit 131 a stops providing the terminal resistor after the transfer period TD1 ends. The terminal circuit 131 b stops providing the terminal resistor after the transfer period TD2 ends. The terminal circuit 131 c stops providing the terminal resistor after the transfer period TD3 ends. Thus, the terminal resistors provided by the terminal circuits 131 a˜131 c will not be connected in parallel via the multi-drop bus 11. After the transmission of the video data is completed, all terminal circuits stop providing the terminal resistor.

Refer to FIG. 2, FIG. 4 and FIG. 5 at the same time. FIG. 4 is a schematic diagram of a terminal circuit according to a first embodiment. FIG. 5 is a schematic diagram of a setting command according to a first embodiment. The circuit design of the terminal circuits 131 b and 131 c can be identical to that of the terminal circuit 131 a. The setting command C1 comprises a switch signal Ssw and selection signals SEL0 and SEL1. The terminal circuit 131 a comprises resistors R1˜R6, a selection circuit and a switch SW. The switch signal Ssw is used for controlling the switch SW. The resistors R1˜R3 have different resistances, and the resistors R4˜R6 have different resistances. The selection circuit comprises multiplexers M1˜M4.

During the setting period TS1, the multiplexers M1 and M2 select one of the resistors R1˜R3 as the first candidate resistor according to the selection signal SEL0 of the setting command C1. During the setting period TS1, the multiplexer M3 and M4 select one of the resistors R4˜R6 as the second candidate resistor according to the selection signal SEL1 of the setting command C1. During the setting period TS1, the switch SW is turned on according to the switch signal Ssw of the setting command C1 to provide a terminal resistor. During the setting period TS1, if the multiplexer M1 and M2 select the resistor R1 as the first candidate resistor and the multiplexer M3 and M4 select the resistor R4 as the second candidate resistor, then the terminal resistor provided by the terminal circuit 131 a is a serial connection of resistors R1 and R4.

Refer to FIG. 1, FIG. 4 and FIG. 6 at the same time. FIG. 6 is a schematic diagram of all terminal circuits concurrently providing terminal resistors. The terminal circuits 131 a˜131 c respectively provide terminal resistors RT1˜RT3. Two ends of the terminal resistors RT1˜RT3 are concurrently coupled to the multi-drop bus 11. The terminal resistors RT1˜RT3 can be formed by a combination of resistors R1˜R6. For example, the terminal resistor RT1 can be realized by a serial connection of resistors R1 and R4. The terminal resistor RT2 can be realized by a serial connection of resistors R2 and R5. The terminal resistor RT3 can be realized by a serial connection of resistors R3 and R6. The terminal resistor RT1 and the terminal resistors RT2 and RT3 can be connected in parallel via the multi-drop bus 11. The terminal circuits 141 a˜141 c respectively provide terminal resistors RT4˜RT6, and two ends of terminal resistors RT4˜RT6 are concurrently coupled to the multi-drop bus 12. The terminal resistor RT4 and the terminal resistors RT5 and RT6 can be connected in parallel via the multi-drop bus 12.

Refer to both FIG. 1 and FIG. 7. FIG. 7 is a schematic diagram of some of the terminal circuits providing a terminal resistor. The terminal circuits 131 b, 131 c, 141 a and 141 b respectively provide terminal resistors RT2, RT3, RT4 and RT5. The terminal circuits 131 a and 141 c do not provide terminal resistors RT1 and RT6. Two ends of the terminal resistors RT2 and RT3 are concurrently coupled to the multi-drop bus 11, and so are two ends of the terminal resistor RT4 and terminal resistor RT5 concurrently coupled to the multi-drop bus 12. Two ends of the terminal resistor RT1 are not concurrently coupled to the multi-drop bus 11, and nor are two ends of the terminal resistor RT6 concurrently coupled to the multi-drop bus 12.

Refer to both FIG. 1 and FIG. 8. FIG. 8 is a schematic diagram of all terminal circuits concurrently not providing any terminal resistors. The terminal circuits 131 a˜131 c do not provide terminal resistors RT1˜RT3 respectively. The terminal circuits 141 a˜141 c do not provide terminal resistors RT4˜RT6 respectively. Two ends of the terminal resistor RT1 are not concurrently coupled to the multi-drop bus 11, and nor are two ends of the terminal resistor RT2 concurrently coupled to the multi-drop bus 11. Two ends of the terminal resistor RT3 are not concurrently coupled to the multi-drop bus 11, and nor are two ends of the terminal resistor RT4 concurrently coupled to the multi-drop bus 12. Two ends of the terminal resistor RT5 are not concurrently coupled to the multi-drop bus 12, and nor are two ends of the terminal resistor RT6 concurrently coupled to the multi-drop bus 12.

Second Embodiment

Refer to both FIG. 2 and FIG. 9. FIG. 9 is a timing diagram of video data transmission according to a second embodiment. The second embodiment is different from the first embodiment mainly in that during the setting period TS1, each of the terminal circuits 131 a, 131 b and 131 c provides a terminal resistor according to the setting command C1 and further connects the terminal resistor to the multi-drop bus 11. Furthermore, the receiving circuit 1321 a receives the setting command C1 via the multi-drop bus 11 during the setting period TS1 and receives the video data D1 via the multi-drop bus 11 during the transfer period TD1. During the setting period TS1, each of the terminal circuits 131 a, 131 b and 131 c provides a terminal resistor according to the setting command C1 and further connects the terminal resistor to the multi-drop bus 11. The driving signal generator 1322 a outputs a corresponding source driving signal according to the video data D1. After the transfer period TD1 ends, the source driving chip 13 a outputs the data input/output starting signal DIO1 to the source driving chip 13 b.

After the data input/output starting signal DIO1 activates the source driving chip 13 b, the receiving circuit 1321 b receives the video data D2 via the multi-drop bus 11 during the transfer period TD2. The transfer period TD2 is behind transfer period TD1. The driving signal generator 1322 b outputs a corresponding source driving signal according to the video data D2. After the transfer period TD2 ends, the source driving chip 13 b outputs the data input/output starting signal DIO2 to the source driving chip 13 c. After the data input/output starting signal DIO2 activates the source driving chip 13 b, the receiving circuit 1321 c receives the video data D3 via the multi-drop bus 11 during the transfer period TD3. The transfer period TD3 is behind the transfer period TD2. The driving signal generator 1322 c outputs a corresponding source driving signal according to the video data D3.

Third Embodiment

Refer to FIG. 2, FIG. 4, FIG. 5, FIG. 10 and FIG. 11 at the same time. FIG. 10 is a schematic diagram of a terminal circuit according to a third embodiment. FIG. 11 is a schematic diagram of a setting command according to a third embodiment. The third embodiment is different from the first embodiment mainly in that the terminal circuit 131 a of the third embodiment does not comprise the multiplexers M3˜M4 or the resistors R4˜R6, and the setting command C1 of the third embodiment does not comprise the selection signal SEL1. During the setting period TS1, the multiplexers M1 and M2 select one of the resistors R1˜R3 as a terminal resistor according to the selection signal SEL0 of the setting command C1. During the setting period TS1, the switch SW is turned on according to the switch signal Ssw of the setting command C1 to provide a terminal resistor.

Fourth Embodiment

Refer to both FIG. 1 and FIG. 12. FIG. 12 is a schematic diagram of a video transmission system according to a fourth embodiment. The fourth embodiment is different from the first embodiment mainly in that the video transmission system 4 further comprises impedance matching elements 111 and 121. The impedance matching elements 111 and 121 can both be realized by such as a resistor, a capacitor or an inductor. The impedance matching element 111 is disposed in the multi-drop bus 11, and the impedance matching element 121 is disposed in the multi-drop bus 12. In addition to using the terminal resistors provided by the source driving chips 13 a˜13 c and the source driving chips 14 a˜14 c, the video transmission system 4 can further use the impedance matching elements 111 and 121 disposed outside the source driving chips 13 a˜13 c and the source driving chips 14 a˜14 c to increase the flexibility in the adjustment of impedance matching.

Fifth Embodiment

Refer to both FIG. 1 and FIG. 13. FIG. 13 is a schematic diagram of a video transmission system according to a fifth embodiment. The fifth embodiment is different from the first embodiment mainly in that the video transmission system 5 further comprises an impedance matching element 111, a terminal resistor 112, an impedance matching element 121 and a terminal resistor 122, and that the multi-drop bus 11 of the video transmission system 5 further comprises transmission lines 11 c˜11 f and transmission lines 12 c˜12 f. The impedance matching element 111 is disposed between transmission lines 11 c and 11 d. The impedance matching element 121 is disposed between the transmission lines 12 c and 12 d. The impedance matching element 111 can be incorporated with the impedance matching between the terminal resistor provided by the source driving chips 13 a˜13 c and the transmission lines 11 c and 11 d. The impedance matching element 121 can be incorporated with the impedance matching between the terminal resistor provided by the source driving chips 14 a˜14 c and the transmission lines 12 c and 12 d. The terminal resistor 112 is disposed between the transmission lines 11 e and 11 f. The terminal resistor 122 is disposed between the transmission lines 12 e and 12 f. The terminal resistor 112 is used for matching impedance with the transmission lines 11 e and 11 f. The terminal resistor 122 is used for matching impedance with the transmission lines 12 e and 12 f.

When a printed circuit board has a terminal resistor disposed therein, signals entering the source driving chip still have to pass through an impedance mismatching path, and the signals received by the source driving chip will be distorted. According to the video transmission system disclosed in above embodiments, terminal resistors are embedded in the source driving chip, hence shortening the impedance mismatching path and avoiding the signals received by the source driving chip being distorted. Besides, since the source driving chips are disposed at different positions, the resistances of the transmission lines between the timing controller and different source driving chips will be different accordingly. The terminal circuits disclosed in above embodiments are capable of flexibly adjusting the resistance of each terminal resistor, such that the source driving chips can achieve suitable impedance matching with the transmission lines.

While the invention has been described by way of example and in terms of the preferred embodiment (s), it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures. 

What is claimed is:
 1. A video transmission system, comprising: a multi-drop bus, comprising at least one first transmission line and at least one second transmission line; a timing controller; a first source driving chip, coupled to the timing controller via the at least one first transmission line of the multi-drop bus and comprising: a first source driving circuit, and a first terminal circuit embedded in the first source driving chip and coupled to the multi-drop bus and the first source driving circuit for providing a first terminal resistor with a first adjustable resistance that is set in response to a first setting command output by the timing controller during a first setting period, wherein the first setting period is before a first transfer period during which the timing controller transfers first video data to the first source driving circuit; and a second source driving chip, coupled to the timing controller via the at least one second transmission line of the multi-drop bus and comprising: a second source driving circuit; and a second terminal circuit embedded in the second source driving chip and coupled to the multi-drop bus and the second source driving circuit for providing a second terminal resistor with a second adjustable resistance that is set in response to a second setting command output by the timing controller during a second setting period, the second setting period being before a second transfer period during which the timing controller transfers second video data to the second source driving circuit, wherein the first adjustable resistance and the second adjustable resistance are set for impedance matching with the at least one first transmission line and the at least one second transmission line.
 2. The video transmission system according to claim 1, wherein the first source driving circuit further comprises: a first receiving circuit used for receiving the first setting command via the multi-drop bus during the first setting period and receiving the first video data via the multi-drop bus during the first transfer period, wherein the first setting period and the first transfer period are within a frame period, and a first driving signal generator used for outputting a plurality of first source driving signals according to the first video data, wherein the first terminal circuit further connects the first terminal resistor to the multi-drop bus during the first setting period.
 3. The video transmission system according to claim 2, wherein the first source driving circuit further comprises: a first register used for storing the first setting command.
 4. The video transmission system according to claim 2, wherein the first terminal circuit stops providing the first terminal resistor after the first transfer period ends.
 5. The video transmission system according to claim 2, wherein the first terminal circuit comprises: a plurality of first resistors having different resistances; and a selection circuit used for selecting some of the first resistors as the first terminal resistor according to the first setting command during the first setting period; and a switch used for providing the first terminal resistor according to the first setting command.
 6. The video transmission system according to claim 5, wherein the first setting command comprises a first selection signal, and the selection circuit comprises: a first multiplexer; and a second multiplexer, wherein the second multiplexer and the first multiplexer together select one of the first resistors as the first terminal resistor according to the first selection signal.
 7. The video transmission system according to claim 6, wherein the first setting command further comprises a switch signal used for controlling the switch.
 8. The video transmission system according to claim 5, wherein the first terminal circuit further comprises a plurality of second resistors having different resistances, the first setting command comprises a first selection signal and a second selection signal, and the selection circuit comprises: a first multiplexer; a second multiplexer, wherein the first multiplexer and the second multiplexer together select one of the first resistors a first candidate resistor according to the first selection signal; a third multiplexer; and a fourth multiplexer, wherein the fourth multiplexer and the third multiplexer together select one of the second resistors as a second candidate resistor according to the second selection signal, and the switch electrically connects the first candidate resistor and the second candidate resistor to provide the first terminal resistor.
 9. The video transmission system according to claim 8, wherein the first setting command further comprises a switch signal used for controlling the switch.
 10. The video transmission system according to claim 2, wherein the second source driving circuit comprises: a second receiving circuit used for receiving the second setting command via the multi-drop bus during the second setting period and receiving the second video data via the multi-drop bus during the second transfer period, wherein the second setting period is behind the first transfer period; and a second driving signal generator used for outputting a plurality of second source driving signals according to the second video data; wherein, during the second setting period, the second terminal circuit connects the second terminal resistor to the multi-drop bus.
 11. The video transmission system according to claim 10, wherein the second source driving circuit further comprises: a second register used for storing the second setting command.
 12. The video transmission system according to claim 10, wherein the second terminal circuit stops providing the second terminal resistor after the second transfer period ends.
 13. The video transmission system according to claim 2, wherein the second source driving circuit comprises: a second receiving circuit used for receiving the first setting command via the multi-drop bus during the first setting period and receiving the second video data via the multi-drop bus during the second transfer period behind the first transfer period; and a second driving signal generator used for outputting a plurality of second source driving signals according to the second video data; wherein, during the first setting period, the second terminal circuit provides the second terminal resistor according to the first setting command and further connects the second terminal resistor to the multi-drop bus.
 14. The video transmission system according to claim 13, wherein the second terminal circuit stops providing the second terminal resistor after the second transfer period ends.
 15. The video transmission system according to claim 1, further comprising: an impedance matching element disposed in the multi-drop bus.
 16. The video transmission system according to claim 1, wherein two ends of the first terminal resistor are concurrently coupled to the multi-drop bus, and so are two ends of the second terminal resistor concurrently coupled to the multi-drop bus.
 17. The video transmission system according to claim 1, wherein two ends of the first terminal resistor are concurrently coupled to the multi-drop bus, but two ends of the second terminal resistor are not concurrently coupled to the multi-drop bus.
 18. The video transmission system according to claim 1, wherein two ends of the first terminal resistor are not concurrently coupled to the multi-drop bus, and nor are two ends of the second terminal resistor concurrently coupled to the multi-drop bus.
 19. The video transmission system according to claim 1, wherein the first adjustable resistance and the second adjustable resistance are set to different values depending upon different resistances of the at least one first transmission line and the at least one second transmission line.
 20. The video transmission system according to claim 1, wherein the first terminal circuit provides the first terminal resistor with the first adjustable resistance during at least the first transfer period, and the second terminal circuit provides the second terminal resistor with the second adjustable resistance during at least the second transfer period.
 21. The video transmission system according to claim 20, wherein the first terminal circuit stops providing the first terminal resistor with the first adjustable resistance after the first transfer period, and the second terminal circuit stops providing the second terminal resistor with the second adjustable resistance after the second transfer period.
 22. The video transmission system according to claim 20, wherein the first terminal circuit continually provides the first terminal resistor with the first adjustable resistance after the first transfer period or during the second transfer period.
 23. The video transmission system according to claim 1, wherein the first setting command and the second setting command are inserted in a signal transmitted from the timing controller to the first source driving circuit and the second source driving circuit, and the signal includes the first video data and the second video data.
 24. The video transmission system according to claim 1, wherein each of the first and second adjustable resistances is set from multiple resistance values by the first setting command and second setting command, respectively. 